Evaluation of the efficacy of commercial sanitizers against adhered and planktonic cells of Listeria monocytogenes and Salmonella spp

Recent advances on the formation, detection, resistance mechanism, and control technology of Listeria monocytogenes biofilm in food industry

Listeria monocytogenes is an important foodborne pathogen that causes listeriosis, a severe and fatal condition. Biofilms are communities of microorganisms nested within a self-secreted extracellular polymeric substance, and they protect L. monocytogenes from environmental stresses. Biofilms, once formed, can lead to the persistence of L. monocytogenes in processing equipment and are therefore considered to be a major concern for the food industry. This paper briefly introduces the recent advancements on biofilm formation characteristics and detection methods, and focuses on analysis of the mechanism of L. monocytogenes biofilm resistance; Moreover, this paper also summarizes and discusses the existing different techniques of L. monocytogenes biofilm control according to the physical, chemical, biological, and combined strategies, to provide a theoretical reference to aid the choice of effective control technology in the food industry.

Condensation Removal Practices and Their Potential for Contributing to Environmental Pathogen Contamination in Food Processing Facilities

ABSTRACT

Food manufacturers often use squeegees as a tool to remove condensation from overhead surfaces. This practice is done to reduce the likelihood of environmental pathogen contamination by eliminating condensed-water droplets that could fall from overhead surfaces during production. However, this practice may actually spread environmental pathogens across these surfaces, defeating its purpose and further increasing the risk for contamination in the processing area. To understand the risk associated with this common practice, test pipes inoculated with Listeria innocua ATCC 33090 were exposed to steam to produce condensation, which was then removed by squeegees. The pipe surfaces, droplets, and squeegees were subsequently analyzed for Listeria to determine the distance the organism spread across the pipe and how many organisms were transferred to the droplets and the squeegees. Results showed that Listeria traveled as far as 16 in. across the surface of the pipe, and bacterial transfer to the droplets decreased as the squeegee traveled further from the contaminated area. Sanitizers alone were able to remove about 1 to 2 log CFU of Listeria per in2 from the squeegee blades when materials were contaminated with Listeria (>6 log CFU/in2). Among the cleaning protocols evaluated, an extensive cleaning regimen was able to remove 3 to 4 log CFU/in2, which would be recommended to reduce the risk associated with environmental pathogen transfer. This study provides evidence that supports recommendations for minimizing the cross-contamination risk associated with condensation management practices.

HIGHLIGHTS

Bacterial biofilm formation on stainless steel in the food processing environment and its health implications

Biofilm formation (BF) and production in the food processing industry (FPI) is a continual threat to food safety and quality. Various bacterial pathogens possess the ability to adhere and produce biofilms on stainless steel (SS) in the FPI due to flagella, curli, pili, fimbrial adhesins, extra polymeric substances, and surface proteins. The facilitating environmental conditions (temperature, pressure, variations in climatic conditions), SS properties (surface energy, hydrophobicity, surface roughness, topography), type of raw food materials, pre-processing, and processing conditions play a significant role in the enhancement of bacterial adhesion and favorable condition for BF. Furthermore, biofilm formers can tolerate different sanitizers and cleaning agents due to the constituents, concentration, contact time, bacterial cluster distribution, and composition of bacteria within the biofilm. Also, bacterial biofilms' ability to produce various endotoxins and exotoxins when consumed cause food infections and intoxications with serious health implications. It is thus crucial to understand BF's repercussions and develop effective interventions against these phenomena that make persistent pathogens difficult to remove in the food processing environment.

New approach for the removal of mature biofilms formed by wild strains of Listeria monocytogenes isolated from food contact surfaces in an Iberian pig processing plant

One of the main objectives of the food industry is to guarantee food safety by providing innocuous food products. Therefore, this sector must consider all the possible biotic or abiotic contamination routes from the entry of raw materials to the release of the final product. Currently, one important problem in this regard is the presence of biofilms on food contact surfaces which can transmit pathogens such as L. monocytogenes. In industrial conditions biofilms are found in a mature state, so it is essential that when carrying out removal effectiveness studies in vitro the tests are realized with models that produce these structures in a similarly mature state. The main objective of this study was to evaluate the effectiveness of an alternative treatment (i.e. enzymatic detergent that include natural antimicrobial agents) and a conventional treatment (i.e. chlorinated alkaline) for the elimination of mature L. monocytogenes biofilms. The results showed a cell detachment from the formed mature biofilms with an effectivity of between 74.75%-97.73% and 53.94%-94.02% for the enzymatic treatment and the chlorinated alkaline detergent, respectively. On a qualitative level, it was observed that the dispersion in the structure was much higher for the enzymatic treatment than for the chlorinated alkaline, which continued to show obvious structure integrity. All this leads to the conclusion that treatments with an enzymatic detergent have a significantly greater impact on the removal of mature L. monocytogenes biofilms, although a further disinfection process would be needed, enhancing even more the treatment effectivity. This may imply that the industrial approach to addressing this problem should be modified to include new perspectives that are more effective than traditional ones.

Carvacrol encapsulation into nanostructures: Characterization and antimicrobial activity against foodborne pathogens adhered to stainless steel

Carvacrol is a natural antimicrobial capable of inhibiting several microorganisms. The encapsulation of this compound may increase its stability, water solubility and provide controlled release. In this study, carvacrol encapsulated into nanoliposomes (NLC) and polymeric Eudragit® nanocapsules (NCC) was tested against Staphylococcus aureus, Listeria monocytogenes, Escherichia coli and Salmonella spp. adhered to stainless steel. NLC showed an average diameter of 270.8 nm, zeta potential of +8.64 mV, and encapsulation efficiency of 98%. Minimum Bactericidal Concentration (MBC) of NLC was 3.53 mg/mL against Salmonella and 5.30 mg/mL against the other bacteria. NCC presented an average diameter of 159.3 nm, zeta potential of +44.8 mV, and encapsulation efficiency of 97%. MBC of NCC was 4.42 mg/mL against E. coli and 3.31 mg/mL against the other bacteria. After 2 h incubation with NCC at carvacrol concentration equivalent to ½ MBC, viable counts of Salmonella and E. coli were below the detection limit (1.69 CFU/mL). The population of L. monocytogenes and S. aureus was reduced by 2 log CFU/mL in 6 h. Afterwards, pools of each bacterium were separately adhered to stainless steel coupons (initial population 6.5 CFU/cm²). Salmonella and E. coli were inhibited below the detection limit using the NCC at concentration equivalent to MBC, while L. monocytogenes and S. aureus were reduced by 4 log CFU/cm² and 3.5 log CFU/cm², respectively. Although free carvacrol presented better results than encapsulated one in all tests performed, using encapsulated carvacrol could be more interesting for food applications by masking the strong aroma of the compound, in addition to a controlled release of carvacrol. The results suggest that NCC have potential for use in food contact surfaces in order to avoid bacterial adhesion and subsequent biofilm formation.

Experimental approach for a possible integrated protocol to determine sanitizer activity against both planktonic bacteria and related biofilms

The persistence of pathogenic bacteria in industrial settings is linked to biofilm embedded bacteria resistance to antimicrobial and disinfectant methods effective against planktonic cells. We proposed an experimental approach to evaluate sanitizers effectiveness against both planktonic microorganisms and related biofilms as possible integration of the official EN 1276 procedure. Firstly, the efficacy of three chemicals sanitizers was tested on planktonic cells of Escherichia coli O157:H7 ATCC 35150, Staphylococcus aureus ATCC 43387, Pseudomonas aeruginosa ATCC 9027, Enterococcus faecalis ATCC 29212 and Candida albicans ATCC 14053 using the suspension test indicated by EN 1276 in both dirty and clear simulated conditions (0.3% or 0.03% of bovine serum albumen). The sanitizers were tested against the related biofilms developed on stainless steel for 48 h at room temperature. The sanitizers (SANI 626, SUPERIG, IGIEN 155) reached 5-logarithmic reduction at the manufacture's recommended concentrations after 30 s and 5 min against planktonic microorganisms but, sometimes, the organic load interfered with their activity. The same concentrations tested with the proposed protocol weren't effective against biofilms and a log reduction >3 was reached using higher concentrations of the sanitizers and 15 min of contact, with the exception of IGIEN 155. The efficacy of a disinfectant/sanitizer is assessed against planktonic microorganisms and bacteria adhered to surface, while those embedded in biofilms are not taken into consideration. The proposed protocol could be used to evaluate the effectiveness of a sanitizer also against microorganisms organized in biofilms, in order to give to the users more detailed information on its activity.

The testing of sanitizers efficacy to enterococci adhered on glass surfaces

The aim of this work was to test the ability of 6 strains of enterococci to adhere on glass surfaces in environment with different content of milk residues and then to evaluate efficacy of 2 commercial sanitizers (alkaline and acidic) used in milk production. Tested enterococci were isolated from milk, dairy products and from rinse water after sanitation milking machine. Suspension of enterococci (8 log CFU.ml-1) was prepared in phosphate buffered saline (PBS), PBS with content 0.1% and 1% of skimmed reconstituted milk. Glass plates were immersed into bacterial suspension for 1 h at 37 °C. The number of enterococci adhered on glass surface in PBS achieved an average value 3.47 log CFU.mm-2, in PBS with 0.1% of milk 2.90 CFU.mm-2, in PBS with 1% of milk 2.63 CFU.mm-2. Differences between the tested files were not statistically significant (p >0.05). In the second part of work the glass plates with adhered enterococci were exposed to the effect of alkaline sanitizer (on basis of NaOH and NaClO), respectively acidic sanitizer (on basis of H3PO4). Sanitation solutions were prepared and tested according to manufacturer recommendations (concentration 0.25%, contact time 20 min, temperature   20 °C). Alkaline sanitation solution was 100% effective against all tested enterococci regardless to content of milk residues in environment. Acidic sanitation solution was 100% effective only against E. faecalisD (isolated from rinse water after sanitation). Average value of reduction of enterococci with acidic sanitation solution, which were on glass plates in environment PBS was 2.84 CFU.mm-2, in PBS with 0.1% of milk was 2.45 CFU.mm-2 and in PBS with 1% of milk was2.16 CFU.mm-2. It can be concluded, that increase of milk residues in environment decrease the adhesion of enterococci on glass surface, but also effectiveness of acidic sanitation solution.

The Elimination of Listeria Monocytogenes Attached to Stainless Steel or Aluminum Using Multiple Hurdles

Ready-to-eat luncheon meats sliced in retail delis have been found to pose the greatest risk of foodborne illness from Listeria monocytogenes among all ready-to-eat foods. Slicers used in delis have many removable parts that are connected with seals and gaskets, with spaces, cracks and crevices that are difficult to clean adequately and may provide a niche for L. monocytogenes survival. Standard cleaning and sanitizing practices used by deli employees may not eliminate Listeria in these niches. Moist heat is known to be more effective against L. monocytogenes than dry heat at the same temperature and time. The study reported here investigated the effects of moist heat combined with quaternary ammonium compounds (5 or 10 ppm), chlorine (10 or 25 ppm) or peracetic acid (10 or 25 ppm) on inactivating L. monocytogenes attached to stainless steel or aluminum coupons cut from commercial deli meat slicer components. All sanitizers when used alone resulted in a 2- to 3-log reduction of L. monocytogenes on stainless steel or aluminum surfaces, while moist heat alone resulted in a 3- to 4-log reduction. When combined with heat the quaternary ammonium was used at 5 ppm, peracetic acid at 10 ppm and chlorine at 10 ppm. When the 2 lethal treatments were combined there was a 5- to7-log reduction as compared to initial inoculation.

PRACTICAL APPLICATION

The results of this study will provide a better understanding and potential methods for the sanitization of industrial deli meat slicers. In turn, the knowledge gained from this study can reduce the risk of contamination and outbreaks of L. monocytogenes and other food-borne pathogens for consumers.